1. Field of the Invention
The present invention relates to structures, structures to which anodized alumina nano-holes are applied, production methods thereof, electron-emitting devices, and image-forming apparatus. Particularly, the structures of the present invention can be applied to electron-emitting devices, image-forming apparatus, electrochromic devices, imaging tubes, and so on.
2. Related Background Art
Considerable research is now under way on the electron-emitting devices having the properties of uniformity, fineness, high efficiency, and long life, as typified by flat panel displays. For forming microscopic electron-emitting regions of the devices, a lot of processes are performed by making use of the semiconductor processing techniques including photolithography, electron beam exposure, and so on.
However, application of materials having microscopic structure (nano-structures) can be listed as a simple method of forming the electron-emitting regions uniformly and in a large area. Particularly, attention is being drawn to structures formed in a self-organizing manner.
For the nano-structures, it is preferable to employ a porous film of alumina obtained by anodization of aluminum. First, the anodization of aluminum has such features that, when it is done in an aqueous solution of oxalic acid, phosphoric acid, or sulfuric acid, pores (nano-holes) are formed in nano-size so as to be surrounded by a barrier layer (alumina), thereby yielding a porous film; and that, when it is done in an aqueous solution of ammonium borate, ammonium tartrate, or ammonium citrate, the pores are not formed but a uniform alumina film (barrier film) is formed, thereby yielding a barrier film.
FIGS. 2A, 2B, and 2C are schematic views of films obtained by the anodization of aluminum, wherein FIG. 2A is a plan view of the porous film, FIG. 2B a cross-sectional view along line 2B—2B of FIG. 2A, and FIG. 2C a cross-sectional view of the barrier film. The porous film of alumina is characterized by having such a specific geometrical structure that extremely fine, cylindrical pores 21 having pore diameters 26 of several nm to several hundred nm are arrayed in parallel at spacing 25 of several ten nm to several hundred nm, as shown in FIGS. 2A and 2B. Then the array spacing of pores can be controlled by adjusting an electric current and a voltage during the anodization.
Concerning this porous film of alumina, there are such attempts that an electron-emitting member is placed inside each of the holes to form an electron-emitting region and one electron-emitting device is constructed of an assembly of plural electron-emitting regions (e.g., Japanese Patent Applications Laid-Open No. 05-211030, Laid-Open No. 10-12124, and so on). This structure is characterized in that the sizes of the holes are very small. This makes use of the advantages that the electron-emitting regions have a small radius of curvature at the tip, so as to facilitate concentration of an electric field, and thus electron emission occurs readily and that the electric current is stable, because one electron-emitting device is constructed of a plurality of electron-emitting regions.
There are, however, demands for decreasing dispersion among the individual electron-emitting regions and distribution of the electric field and for making the production process simpler.